Undermind

David Albert and Barry Loewer have proposed a new interpretation of quantum mechanics which they call the Many Minds interpretation, according to which there are infinitely many minds associated with a given (physical) state of a brain. This interpretation is related to the family of many worlds interpretations insofar as it assumes strictly unitary (Schrödinger) time-evolution of quantum-mechanical systems (no reduction of the wave-packet). The Many Minds interpretation itself is principally motivated by an argument which purports to show that the assumption of unitary evolution, along with some common sense assumptions about mental states (specifically, beliefs) leads to a certain nonphysicalism, in which there is a many-to-one correspondence between minds and brains. In this paper, I critically examine this motivating argument, and show that it depends on a mistaken assumption regarding the correspondence between projection operators and yes/no questions.Thanks to David Albert, Arthur Fine, Martin Jones, and the two anonymous referees for their comments on an earlier version of this paper, and thanks to Jeremy Butterfield, Rob Clifton, Meir Hemmo and David Malament for comments on a revised version. Special thanks to Arthur for several helpful discussions.